SAFETY IN NUMBERS: Stop Time Measurements

Stop-Time Measurements Keep Safeguarding Equipment in Peak Performance

We’ve all heard the phrase “what a difference a day makes,” yet when it comes to industrial safeguarding, the concern isn’t days, hours or even minutes. It is the milliseconds it takes for a machine operation to stop. That fraction of a second can make the difference between a life-changing injury or a safe machine cycle, the difference between a valued employee going home or being taken to the emergency room.

How can we assure the right outcome? How do we determine if a machine will stop in time?

The answer is specialized equipment called “Stop-Time Measurement” devices (STM). An STM is used to determine the total response time from the triggering of a machine’s operating control or a safeguarding device… to the exact moment when a dangerous movement comes to a halt. Take, for example, the time it takes for a press brake cycle to stop when a finger or hand enters the point-of-operation zone, or the time between when a light curtain is activated and when the machine comes to a complete standstill.

Once the stop-time data is captured by an STM in either milliseconds or inches, it is applied to an established formula to calculate the minimum safety distance required to install safety devices. A record of the measurement can be printed out, or alternatively, the device can be plugged into a PC where the measurements can be recorded and documented.

Doing the Math
According to OSHA, the majority of machine-related accidents happen as a result of a reflex action or when the operator is not paying attention. For example, a machine operator may instinctively reach into the machine when there is an issue. Or they will be so focused on a task that they’ll cross the threshold into a hazardous area without being aware of it. In these events, it is critical that a machine’s safety devices stop operations before the hazard is reached. In addition, accidents may not be the fault of the operator at all. There are instances where integrators do not program the field of coverage — the area being monitored by the light curtain, for instance — at the proper safety distance and puts the operator unknowingly at danger.

So what is the correct distance? The basic calculation for ‘safety distance’ comprises approach speed, overall stop time and penetration depth factor.

The standard formula is below:
DS = K (T) + DPF
where:
DS = the safety distance
K = the maximum speed that an individual can approach the hazard
T = the total time to stop the hazardous motion
DPF = the depth penetration factor of the safeguarding device

There are other variations on this calculation; for example, where a light curtain is in operation, the calculation requires both the resolution and the response time of the light curtain to be factored. Most STM devices perform calculations internally so the operator doesn’t need to concern themselves with all the details of the math, only the results to act upon.

In the United States there are two formulas that are used to properly calculate the safety distance. The first, the OSHA formula, is the minimum requirement for the calculation of the safety distance. The second is the ANSI formula, which incorporates additional factors to be considered when calculating the safety distance. Rockford Systems recommends the use of the ANSI system since it is the more comprehensive of the two. The formula is included in ANSI standards B11.19-2010 and Robotic Industries Association (RIA) R15.06-1999 (R2009), as well as CSA Z142-10, Z432-04 and Z434-03.

Stop-Time Measurement Service
For all linear and rotating motion equipment, Rockford Systems offers STM service for newly installed safety devices as well as for the periodic validation of existing safety devices. Periodic safety distance validation with an STM is required for AOPD systems, light curtains, 2-hand control systems, emergency stop devices, pressure-sensitive protective strips or mats, interlocking guards, doors and gates, as well as other safety devices and controls equipment used during production. This is necessary since factors like maintenance, brake wear, and alterations can increase the machine’s stopping time. If a machine stops slower than it did when it was originally commissioned then components will need to be adjusted to continue providing the correct level of safety. Stop time measurement is able to detect changes at an early stage, so that appropriate action can then be taken. For these and other reasons it is important to perform at least an annual stop time analysis. Rockford Systems STM services are mainly employed on reciprocating (stroking or cycling) machines, such as mechanical or hydraulic presses and press brakes, but can also be used on machines that rotate, such as lathes, mills, and drills.

Location of a safety component, whether hard guarding or electronic, is based upon the machine’s stopping time. Simply stated, a safety component should be placed far enough away from the risk area that it is not possible to reach the hazard before the machine has stopped. Safety devices are then installed using the minimum safe distance. Reference our OSHA Safety Distance Guide Slide Chart.

Regularly checking shop machinery with Stop-Time Measurements and maintaining a log of the results empowers a company to be proactive in establishing a safety maintenance program. It ensures that safeguarding equipment on machinery works as designed to achieve greater worker safety, productivity and profits.

Lack of Machine Guarding Again Named to OSHA’S Top 10 Most Cited Violations List

Every year around this time, the awards season kicks off with the Emmys, Golden Globes and the grand daddy of them all, the Oscars, eagerly announcing their lists of nominations. At the same time — and on a far more somber note — another roll call is issued, this one from the Occupational Safety & Health Administration (OSHA). Unlike Hollywood’s awards celebrations, however, no one wants to be nominated for OSHA’s Top Ten Most Cited Violations list, let alone take home the top prize.

OSHA revealed its 2017 Top 10 list at the National Safety Congress & Expo in the Indiana Convention Center. The top ten are:

1. Fall Protection – (1926.501): 6,072 violations
2. Hazard Communication (1910.1200): 4,176 violations
3. Scaffolding (1926.451): 3,288 violations
4. Respiratory Protection (1910.134): 3,097 violations
5. Lockout/Tagout (1910.147): 2,877 violations
6. Ladders (1926.1053): 2,241 violations
7. Powered Industrial Trucks (1910.178): 2,162 violations
8. Machine Guarding (1910.212): 1,933 violations
9. Fall Protection – Training Requirements: 1,523 violations
10. Electrical – Wiring Methods (1910.305): 1,405 violations

While reviewing the list, it is important to remain aware that the Federal Occupational Safety & Health Administration (OSHA) is a small agency. When tallied up to include its state partners, OSHA only has 2,100 inspectors who responsible for the health and safety of 130 million American workers, employed at more than 8 million work sites. This translates to about one compliance officer for every 59,000 workers. As a result, some serious injuries are not reported and thousands of potential violations go without citation or fines. In fact, numerous studies have shown that government counts of occupational injury are underestimated by as much as 50 percent. Employers are required to record all injuries meeting the OSHA’s ‘recordable injury’ criteria (except minor first-aid cases) on the OSHA 300 Log, and those meeting the ‘reportable’ criteria (e.g., hospitalizations or deaths), are to be reported to OSHA immediately, or within 24 hours of occurrence, as per the criteria defined in 29 CFR 1904. But it doesn’t mean all of them do.

MACHINE (UN)SAFEGUARDING IN TOP 10 MOST CITED VIOLATIONS
The absence of required machine safeguarding remains a perennial member of OSHA’s Top 10 Most Cited Violations, and 2017 was no exception. It was named number eight on the list with a total of 1,933 violations. These violations refer to OSHA 1910.212 for failing to have machines and equipment adequately guarded. Any machine part, function, or process that might cause injury should be safeguarded. When the operation of a machine may result in a contact injury to the operator or others in the area, the hazard should be removed or controlled.

A lack of machine safeguarding also held the dubious distinction of making the list of OSHA’s ten largest monetary penalties for the year — not once but four times. In fact, the largest proposed monetary penalty, a staggering $2.6 million (USD), arose from an incident where a worker was crushed to death while clearing a sensor fault in a robotic conveyor belt. OSHA alleges that the company failed to use energy control procedures to prevent robotic machinery from starting during maintenance. The manufacturer also was cited for exposing employees to crushing and amputation hazards as a result of improper machine guarding, plus failing to provide safety locks to isolate hazardous energy.

Despite these headline fines, the repercussions for employers putting workers in harm’s way remain small under the 1970 Occupational Safety and Health Act. The average federal fine for a serious workplace safety violation was $2,402 in fiscal year 2016, according to the most recent report by the AFL-CIO. And the median penalty for killing a worker was $6,500.

According to the most recent Bureau of Labor Statistics data, manufacturing plants reported approximately 2,000 accidents that led to workers suffering crushed fingers or hands, or had a limb amputated in machine-related accidents. The rate of amputations in manufacturing was more than twice as much (1.7 per 10,000 full-time employees) as that of all private industry (0.7). The bulk of these accidents occurred while removing jammed objects from a machine, cleaning or repairing the machine, or performing basic maintenance. These injuries were all largely preventable by following basic machine safeguarding precautions. Rockford Systems is committed to helping organizations reduce injuries and fatalities due to a lack of or non-compliant machine safeguarding. By creating a culture of safety in the workplace, Rockford Systems can help plant managers significantly reduce the number of on-the-job injuries and fatalities that occur annually, plus guard against hefty fines, lost production and increased insurance premiums.

Which leads to the question… “Where do we begin?”

TRAINING AND EDUCATION

Ignorantia juris non excusat (“ignorance of the law excuses not”). Recognizing that education is key to safety, Rockford Systems has offered its Machine Safeguarding Seminars for more than two decades. Thousands of safety professionals have attended the seminars from industries as diverse as aerospace and metal fabrication, to government and insurance.

Held ten times a year at our Rockford, Illinois headquarters, the 2.5 day seminars address key topics in safeguarding with a focus on OSHA 29 CFR and ANSI B-11 standards as they relate to specific machine applications and production requirements. Safeguarding equipment, both old and new, is not only explained in depth in the classroom, but demonstrated under power on the shop floor. Most of these machines are equipped with more than one type of safeguarding product so that attendees can see how different guards and devices can be applied.

Roger Harrison, Director of Training for Rockford Systems and an industrial safeguarding expert with over 25,000 hours of training experience, conducts the Machine Safeguarding Seminar.

>Another valuable educational resource is OSHA-10 General Industry and OSHA-30 General Industry training courses, both of which cover machine guarding. All of our training can be provided at your site, if preferred. To learn more about the Rockford Systems training curriculum, please visit https://www.rockfordsystems.com/seminars/

Rockford Systems also provides a variety of FREE machine safeguarding resources for your organization. Please visit our RESOURCES page to find videos, blogs, quick reference sheets, and more or visit our YouTube channel to download past webinar recordings.

ASSESSMENTS
If your organization is interested in safeguarding solutions, consider a Machine Risk Assessment or Machine Safeguarding Assessment as the critical first step in any machine guarding process as outlined in ANSI B11. Most assessments, but not all, follow the basic steps outlined below.

Step 1 – Provide Machine List
To get started, please provide Rockford Systems a list of all machines (manufacturer, model number, and machine description of each machine) to be assessed. This machine list is needed to determine the estimated resource requirement for the onsite audit. Upon receipt of your machine list, an Assessment Proposal will be provided, generally within 24 hours of receipt. Please email your machine list and any machine photos (optional) to sheryl.broers@rockfordsystems.com.

Step 2 – Schedule Onsite Visit
During the assessment, a machine safeguarding specialist will visit your site and conduct a complete audit of all machines identified on the list and evaluate their compliance in five guarding areas (Safeguards, Controls, Disconnects, Starters, and Covers). The assessment is based on OSHA 1910.212 General Requirements (a)(1), ANSI B11 Safety Standards for Metalworking, ANSI/RIA R15.06-2012 Safety Standards for Industrial Robots, and NFPA 79. If Rockford Systems, LLC has additional specific safeguarding requirements above and beyond OSHA 1910.212 and ANSI B11, please provide them before the site visit and we will incorporate them into the assessment.

Also, during the assessment, we may request copies of electrical, pneumatic and/or hydraulic schematics and operator manuals for specific machines. This information is needed for our Engineering Department to review the control circuit for electrical compatibility of equipment being offered, to verify control reliability of the control circuit, to determine interfacing requirements of suggested equipment. If requested, this information would be needed before advancing to Step 3 below.

Step 3 – Receive Compliance Report and Safeguarding Project Proposal
Upon completion of the assessment, a Compliance Report and Safeguarding Project Proposal will be provided to that identifies where each machine is in, or not in, compliance with the above stated regulations and standards. Where not in compliance, we will suggest guarding solutions to bring the machines into compliance, along with associated costs and timeframes.

We look forward to assisting your organization with its safeguarding needs. A team member will call you within 24 hours to further discuss your needs and applications. We are here to help businesses large and small address machine safety challenges and to remove the burden of managing the growing legal complexity of OSHA, ANSI and NFPA requirements from simple turnkey solutions to build-to-spec customized solutions.

Please contact sheryl.broers@rockfordsystems.com or call 1-815-874-3648 (direct) to get started on an assessment today.

PRODUCTS
If you are looking for Machine Safeguarding Products, please visit our PRODUCTS page that offers over 10,000 safeguarding solutions for drill presses, grinders, lathes, milling machines, press brakes, power presses, radial arm drills, riveters and welders, robots, sanders, saws and more.

RETURN ON INVESTMENT
Not sure if the investment in machine safeguarding provides a return on the investment (ROI), it absolutely does and we can help you calculate it. Please read our detailed blog post on this topic.

For more information on how avoid machine injuries and fatalities, please visit www.rockfordsystems.com.

How To Use a Guard Opening Scale

Point-of-operation barrier guards are essential safeguarding equipment for hazardous industrial processes and machinery such as presses, pumps, motors and drills. When properly installed the barriers prevent a person from placing any part of their body into the point of operation by reaching through, over, under or around the guards to access a hazard. However, because barrier guards are typically constructed out of materials such as wire mesh, expanded metal, rods, or hairpins, most have openings that present the potential for injuries if a person reached through them. As a result, whether the guard is fixed, adjustable, movable, or interlocked, any openings must be measured for compliance with Table O-10 of OSHA 29 CFR 1910.217 (Mechanical Power Presses), current ANSI/CSA standards, or International standard ISO 13857 to determine the safe distance from the hazard.

The critical role of measuring barrier openings falls on a simple but often misunderstood tool: the Guard Opening Scale. Also known as “gotcha sticks,” Guard Opening Scales mimic the human hand and forearm. Over the past 70 years they’ve proven to be the most accurate means of ensuring any opening in a barrier guard will not allow a hazardous zone to be accessed.

HISTORY OF THE GUARD OPENING SCALE
The history of the Guard Opening Scale dates back to 1948. It was then that Liberty Mutual Insurance, joined with the Writing Committee for the ANSI B11.1 Safety Standard on Mechanical Power Presses, engineered a stair-step shaped measurement tool to determine guard-opening size vs. guard distance to the nearest Point of Operation hazard. A rash of injuries to mechanical power press operators who reached through barriers and suffered lacerations, amputations and crushed limbs prompted Liberty Mutual’s actions. Although Guard Opening Scales were first designed for point of operation guards on mechanical power presses, they are now often used on other machines as well.

Originally, the recommended dimensions used for the scale were based upon “average-size hands,” which at the time were a woman’s size 6 glove. ANSI incorporated these dimensions from Liberty Mutual into its 1971 revision of the ANSI B11.1 safety standard for mechanical power presses. In 1995, however, a study entitled “A Review of Machine-Guarding Recommendations” was conducted by Donald Vaillancourt and Stover Snook of Liberty Mutual Research to establish whether the 1948 drawings were consistent with current hand size data, in particular as the data relates to women and minorities who have become more prevalent in manufacturing. Vaillancourt and Snook suggested several important modifications including moving the glove size from a woman’s size 6 to a size 4. Drawings from the study have been adopted in several current ANSI B11-series safety standards for machine tools as well as in the ANSI/RIA R15.06 safety standard for industrial robots and robot systems. OSHA in Table O-10 of OSHA 29 CFR 1910.217 did not, on the other hand, officially adopt the drawings.

OSHA VS. ANSI GUARD OPENING SCALES
OSHA Compliance Officers are usually limited to using OSHA’s own scale, which is referenced by CFR 1910.217, Table 0-10. The ANSI scale is more likely to be used by Insurance Loss Control Engineers in manufacturing plants where smaller hand sizes tend to dominate the employee population. Let’s look at the differences in the two designs:


Note that the OSHA scale locks on the 3rd stair-step on the entrance side, and that the tip of the scale does not reach the die, meaning the test is “passed” for that opening size at that distance away. Also note that the ANSI scale locks on the last stair-step on the entrance side, and that the tip of the scale goes past the die, meaning that the test is “failed” for that opening size at that distance away. That problem can be fixed in one of two ways; move the guard a little further away from the die, or make the adjustable guard opening a little smaller, or some combination of those two.

USING A GUARD OPENING SCALE
A Guard Opening Scale is a two-dimensional representative of an average sized finger, hand and arm. Of course, the human body is not two-dimensional but three-dimensional, thus making its correct use critically important. Follow these simple instructions for proper measurements.

First, place the scaled side perpendicular to the smallest dimension in a hole in the barrier guard material and attempt to insert it towards the hazard. If properly designed, the barrier guard will stop the tip from accessing the hazard area. When multiple openings of various sizes exist in a barrier guard, each must be tested with the tool. The maximum guard opening that OSHA allows is a 6-inch opening at 31.5 inches away. For most people that’s armpit to fingertip. Also, the openings should always be measured empty, not with any material in place. This is based on the logic that personnel may put a hand through the guard opening without material taking up a portion of the space. Remember that Safety Inspectors won’t cut a plant operator any slack because the guard happens to be adjustable. Adjustable guard openings must be measured the same as fixed guard openings.

Please call 1-800-922-7533 or visit rockfordsystems.com for more information.

Safeguarding Mechanical Power Presses

Mechanical power presses (a.k.a. punch presses, stamping presses, flywheel presses), have existed in the U.S. since 1857. They were originally designed as either full-revolution, or part- revolution, both of which still exist, although the latter currently represents an estimated 90 percent of the roughly 300,000 mechanical power presses being used in the United States today.

This blog will address part-revolution presses only. These are often referred to as “air clutch” presses, made by dozens of manufacturers. The idea of safety for these machines has existed since 1922, when the first ANSI B11.1 Safety Standard was developed. The latest version, ANSI B11.1-2009 is the 10th update of that standard. This is generally considered to contain the “Best Safety Practices” for press users.

In the early 1970’s, OSHA promulgated a “machine specific regulation” for mechanical power presses, their CFR SubPart O, 1910.217. Very few changes have been made to that regulation since then. Keep in mind that OSHA’s 1910.217 Regulation was taken from ANSI B11.1 using a version that was freshly updated for OSHA in 1971. ANSI has updated their B11.1 four times since that time. Every update adds new, more stringent requirements than the previous version.

Although many companies have long since met the basic OSHA requirements for their presses, a significant number of those shops have yet to make updates to meet the latest ANSI B11.1 Standard. When OSHA regulations came 46 years ago, press control systems were primarily relay-logic systems, designed to meet OSHA’s initial requirement for “Control Reliability” and “Brake Monitoring.”

Press control systems manufactured in the mid 1980’s and beyond have been mostly solid-state, designed to meet the ANSI Standard concept for the “Performance of Safety Related Functions.” One of the advantages to solid-state controls are the features built-into them. Two of these are a: built-in “Stopping Performance Monitor” and built-in “Stop Time Measurement,” which prevents users from having to use a portable device to determine “Safety Distance” when applying Light Curtain and Two-hand Control devices.

Mechanical Power Presses require some combination of guards and/or devices to reduce or eliminate exposure to hazards at the “point of operation” where the dies close. Safeguarding alternatives include: Point-of-Operation Guards, Awareness Barriers, Light Curtains, and Two-Hand Controls.

1) Point-of-Operation Guards
Point-Of-Operation Guards are typically used for continuous operations where coil-stock feeds into the press as it operates in an uninterrupted mode of operation.

By OSHA’s definition, a guard must prevent people from reaching over, under, through, or around it. (OUTA is an acronym easy to remember; This guard keeps you “OUTA” here.) Guards must meet one of two measurement scales (the OSHA guard opening scale or the ANSI/CSA guard opening scale), to ensure that a small hand can’t reach far enough through any opening to get hurt.

To discourage misuse, hinged or sliding guard sections are often electrically interlocked, so that they remain in position (closed) during press operations. Without interlocks, movable sections can easily be left open, whether intentional or not, leaving Operators and others in the area unprotected.

Guard Interlocks are attached to hinged or moving guard sections, since access to the point-of-operation is most often made through those openings. Interlock attachment is best accomplished with tamper-resistant fasteners to discourage cheating the switch.

Many older guards use simple lever-arm or push-button switches. Not only are these switches easy to cheat with tape or wire, they are also spring-operated, leaving them subject to failure it the spring breaks. Newer switches are free of springs, and use actuators with a unique geometry, making them much more difficult to defeat.

2) Awareness Barriers (for low-level hazards only)
Another common method of safeguarding on coil-fed presses is an “Awareness Barrier” (A/B). They should completely surround press auxiliary equipment with railings, chains, or cables, suspended on floor stations. Although they don’t provide the same level protection as a guard, they do help to limit access to hazards on auxiliary equipment like coil-payoffs, feeds, straighteners, etc.

Awareness Barriers are considered superior to just a yellow line on the floor, because to get beyond the A/B requires an intentional act and some physical contact with them. This means the person is well aware that they are entering a hazard area, contrary to their safety training. Auxiliary equipment may also require that ingoing rolls are covered to prevent entanglement with long hair or loose clothing.

Awareness barriers should also have several Danger or Warning signs attached to them specifying what the hazards are in going beyond the A/Bs. Examples of sign verbiage might include: moving coil stock, ingoing pinch points, sharp edges, tripping hazard, etc.

3) Light Curtains
Light Curtains have been around since the mid-1950’s. They consist of a vertically mounted transmitter and receiver with closely spaced beams of infra-red light, creating a flat sensing-field. When fingers, hands, or arms that reach through that sensing-field, the press cycle is prevented or stopped to avoid operator injury.

One of the reasons that presses make a good application for light curtains is that they can be stopped mid-cycle very quickly. Light curtains can be used for either single or continuous applications. The only thing that light curtains don’t provide is “impact protection” should something break in the point of operation and be ejected in the operator’s direction. Where that’s an issue, poly carbonate shields or guards may be appropriate.

Like any safeguarding device, light curtains should be “function-tested” before every operating shift to ensure that they are continuing to provide protection. Make/model specific “function-test procedures” are usually available on each light curtain manufacturer’s website.

4) Two-Hand Controls
Two-Hand Controls are considered a safer means of cycling a press than a foot-switch because both hands must be in a safe position to use them. When cycling a press with a foot switch, hands can be anywhere. When operating a press in the single-cycle mode of operation, it’s possible to use a two-hand control as a safeguarding device as well. This requires that they meet a list of rules in both OSHA and ANSI.

Ten of the basic requirements for a two-hand control being used as a safeguarding device (in the single-cycle mode of operation) include:
1) protection from unintended operation
2) located to require the use of both hands (no elbow & finger tips)
3) concurrently operated (actuation within half-second of each other)
4) holding-time during the downstroke (hazardous portion of cycle)
5) anti-repeat (push and release both actuators for each single cycle)
6) interrupted stroke protection (for all operating stations)
7) separate set of two-hand controls for each operator
8) mounted at a calculated “Safety Distance” from nearest hazard
9) control system to meet “Performance of Safety Related Functions”
10) Stopping Performance Monitor is also required

When running high-production operations, don’t forget to consider ergonomics when choosing and installing two-hand controls. Several manufacturers of low-force and no-force actuators are on the market.

Also required by OSHA on Mechanical Power Presses is an electrically interlocked “Safety Block” whenever dies are being adjusting or repaired while they are in the press. The interlock is required because safety blocks are very seldom designed to hold the full working-force of the press (please refer to our Die Safety Blocks blog for additional information).

Mechanical Power Presses require two types of OSHA inspections:
1) Periodic and regular (typically quarterly) inspections of the press parts, auxiliary equipment, and safeguards . . . (don’t forget to document)
2) Weekly inspections of; clutch/brake mechanism, anti-repeat feature . . . along with other items (don’t forget to document)

OSHA requires training (in 1910.217) for anyone who cares for, inspects, maintains, or operates mechanical power presses.

ANSI B11.1-2009, requires training for “all (people) associated with press production systems, including operators, die setters, maintenance personnel, supervisors, which must also include (OSHA) 1910.147 Lockout/Tagout.”

Please call 1-800-922-7533 or visit rockfordsystems.com for more information.

Demystifying Die Safety Blocks

OVERVIEW

Picture13Die safety blocks are called by many names: safety blocks, ram blocks, die blocks or prop blocks. Regardless of the term, die safety blocks all have the same purpose: provide protection to anyone working in the die area from a free-falling upper die/slide. This all-too-common accident happens in the event of a brake or counterbalance failure, broken pitman or adjusting screw, or a sudden loss of hydraulic pressure on presses.  While die safety blocks are on the surface simple devices, there are many factors to consider in choosing what type of to use, as well as how many to use or where to put them. As a result many organizations struggle with this topic.

OSHA REGULATIONS

Die safety blocks are required by OSHA CFR 29, Subpart O, 1910.217 (d)(9)(iv) Mechanical Power Presses which states, “The employer shall provide and enforce the use of safety blocks for use whenever dies are being adjusted or repaired in the press.” OSHA does not require the use of safety blocks during die setting; however, companies may include them during die setting procedures as a best safety practice. Proper use of die safety blocks also satisfies OSHA’s lockout/tagout requirements for controlling mechanical energy.

047Anytime an employee needs to put their hands in the die area of a press or is required to work on the die, they must follow OSHA regulations without exception. At no time should the employee make any adjustments or service within the die space area without taking proper protection measures that meet OSHA and ANSI requirements. Regardless of how time-consuming, the company is responsible—and liable—for these procedures in a press shop.

With the press motor off and the flywheel at rest (for mechanical presses), safety blocks are placed between the die punch and holder with the machine stroke up.  The number of safety blocks is determined by the size of the press bed and the weight the blocks must support. On larger presses, the total slide weight must then be distributed among the quantity of safety blocks required.  In some applications, as many as four safety blocks may be required.

The ram is usually adjustable; therefore, wedges or the adjustable screw device is offered to provide a proper fit. If the die takes up most of the space on the die set, it may be difficult to find a place to insert the block. To avoid accidentally stroking the press or leaving the safety block in the die after use, an electrical power cut-off interlock system should be used.

According to ANSI B11.19-2003, safety blocks “shall be interlocked with the machine to prevent actuation of hazardous motion of the machine.” The electrical interlock system for die safety blocks must be interfaced into the control system so that when the plug is pulled, the power to the main drive motor and control is disconnected. If the machine has a mechanical energy source, such as a flywheel, it must come to rest before the die block can be inserted.

DIE SAFETY BLOCK CALCULATIONS

Three factors need to be determined to guide your selection of safety blocks:  static load, block length and block size.

  1. Determine Static Load

The actual static load that the die safety block(s) will support is determined by adding the actual weights of the press slide and slide components (ram-adjustment assembly, connection rod[s] or pitman arm[s], and the upper die).

If this weight cannot be determined, an approximate static load can be calculated using the formula below. Allow 2000 pounds of static load for each cubic foot displaced in the press bed area (front to back x right to left) multiplied by the shut height (die space) of the press. Note: When using this formula, the calculated approximated static load has a safety factor of two (2).

NEW Sfty Blk Shut Hght-01

Allow 2000 pounds of static load for each cubic foot displaced in the press bed area (front to back x right to left) multiplied by the shut height (die space) of the press.  Note:  When using this formula, the calculated approximated static load has a safety factor of two (2).

Static Load Formula:

  • (Press Bed Area (sq in) x Shut Height (in))/(Cubic Inches/Cubic Feet (1728 cu in/cu ft constant))
  • Cubic feet displaced x 2000 lb/cubic foot = Total Static Load

Example:

  • Press Bed Area = 48 in x 96 in
  • Shut Height = 24 in
  • (48 x 96 x 24)/1728 or 110,592/1728 = 64 cu ft
  • 64 cubic feet displaced x 2000 lb/cu ft = 128,000 Total Cubic Static Load
  1. Determine Block Length

With the machine at the top of its stroke; stroke up—adjustment up (S.U.A.U.), measure the space between the upper and lower die set plates (not the distance between the bolster and slide). This gives the maximum safety block length.

To determine the stroke up—adjustment down (S.U.A.D.) measurement, subtract the ram adjustment from the S.U.A.U. figure. This provides the minimum length of the die safety block.

Total Length of Die Safety Block Required ___________”

EXCEPTIONS:

  1. If wedges will be used, subtract 11 ⁄2″ maximum. This is an allowance for variation in the stopping point of the crankshaft or adjustment of the ram.

Total Length of Die Safety Block Required ____________”

  1. When an adjustable screw is added to an octagonal safety block, the minimum length of the aluminum portion of the safety block is as follows:

When an adjustable screw device is added to an octagonal safety block and the screw is all the way inside of the safety block, it will add 2″ to the overall length of small and medium safety blocks and 21 ⁄2″ to the overall length of large safety blocks. Therefore, subtract 2″ for small or medium blocks and 21 ⁄2″ for large blocks to determine the length of the aluminum portion of the die block.

Example:

  • If the minimum overall length of the small or medium safety block required is 101 ⁄2″ with any size adjustable screw device, the aluminum portion of the safety block would be 81 ⁄2″ (101 ⁄2″ – 2″ = 81 ⁄2″).

Example:

  • If the minimum overall length of the large safety block required is 16″ with any size adjustable screw device, the aluminum portion of the safety block would be 131 ⁄2″ (16″ – 21 ⁄2″ = 131 ⁄2″).

Total Length of the Aluminum Portion of the Die Safety Block ___________”

  1. Determine Block Size

The size of the die safety block (small, medium, large) is determined by one or both of the following factors:

  1. The size of the block itself and the area available in the die.
  2. The static load capacity of the block (small, medium, large) versus the total static load being supported.

ROCKFORD SYSTEMS CAN HELP

dsb-shape-collage
Wedge Safety Blocks

Rockford Systems offers a variety of die safety blocks, electrical interlock systems, accessories and operator safety resources.  Our line of high-strength, aluminum wedge die safety blocks that are lightweight and come in several shapes (x-shape, u-shape, octagon shape) and sizes (small, medium, large) to meet every press application. The unique shape and mechanical properties of the 6063-T5 aluminum have been calculated according to stringent structural aluminum design analysis standards to provide high strength.  Blocks are sold in standard 9′ lengths or can be cut to any size.

Rockford Systems also offers adjustable die safety blocks.  These adjustable die safety blocks feature a tough malleable-iron bell-bottom base. The blocks also have a convenient handle for lifting and precision-cut acme threads for easy adjustment and extra rigidity.  The adjusting screw can be easily adjusted up or down by hand. Turning holes are also provided in the screw neck to faciliDie Block-Octagon Static Loadtate the use of a turning bar, if required.

All Rockford Systems static load charts (see example at right) are found on www.rockfordsystems.com on die block product pages.

Die Block Electrical Interlock System
Die Block Electrical Interlock System

Unlike most competitors, Rockford Systems offers electrically interlocked systems.  The interlock system is available in a yellow plug with one contact (KTS518) or an orange plug with two contacts (KTS533). The electrical interlock system for die safety blocks includes the plug, a 24-inch long chain, a receptacle, and an electrical mounting box.

Additional die block accessories available from Rockford Systems include lifting handles, holders and bases.  Our octagon shape safety block comes with an optional heavy-duty steel, adjustable screw device to prevent any space between the block and die when various dies are used or when the slide is adjusted.

Danger Sign for Die Safety Blocks
Don’t forget to post the appropriate danger signs near all machinery in the plant. The purpose of danger signs is to warn personnel of the danger of bodily injury or death. The suggested procedure for mounting this sign is as follows:
1) Sign must be clearly visible to the operator and other personnel
2) Sign must be at or near eye level
3) Sign must be PERMANENTLY fastened with bolts or rivets

Click HERE to watch the Die Safety Block Video Demonstration.

Please call 1-800-922-7533 or visit www.rockfordsystems.com for more information.