BLM Succeeds in United States and Canadian Markets, Metallurgy Important in Centrifugal Operation

SIXTEEN YEARS AGO a Toronto inventor came up with an idea for an automatic clutch a new idea based on an old principle, an idea so mechanically sound that is seemed almost simple. It wasn't, but today there are 15,000 of N. Bruce Wilson's BLM automatic clutches operating in Canadian industry. Seven patents protect the ideas he thought of in 1933 and developed over the years. The Hardinge Co. in York, Pa., produces the clutch under license for the United States market. Fifteen agencies handle the product in other countries. And the Canadian company, the Automatic Clutch Corp. which manufactures for Canada and this foreign market is still Bruce Wilson's baby. He owns it lock, stock and patents just the way he planned it.

Those sixteen years have produced an ever increasing demand for Bruce Wilson's clutch and an ever-better product. There was never any serious mechanical problem. The idea, as he says, was "completely natural and logical." Wilson's job was to find the metals and alloys that would perform, effectively and safely, the demanding tasks he required.

Simplicity of design and operation is the principle of Wilson's clutch. The BLM is an automatic centrifugal clutch. There are three major parts -a drive body, driving mechanism and driven body. The circular, plate-like drive body has eight bosses evenly spaced about the perimeter. The driving mechanism, is composed of eight metal blocks mounted on a spider ring and joined together by loose lateral pins forming a uniform expansion ring. As the prime mover picks up speed, the mechanism automatically expands outward, the blocks riding up between the bosses. This simple centrifugal action transmits the power of the inner wall of the driven body, through non-asbestos linings.

The clutch eliminates damage from starting shock. The clutch mechanism takes hold gradually until the speed of the driven body reaches the rated speed of the power unit. In many installations the period of start for the load is two minutes or more, during which time the power unit is running at its rated speed, the clutch slipping the overload and gradually accelerating the load until the driven machine and the power unit are running in unison.

It is designed to transmit a definite torque or horsepower at a given speed. Any load over the rating causes the clutch automatically to slip, eliminating dangerous overloads that might cause damage or delayed production.

It operates vertically, horizontally or at any angle, and can be used with electrical, gasoline or diesel power units, from fractionals to 5,000 hp and over.

Mr. Wilson saw from the start that metallurgy would be a prime factor in translating his idea to a reality. He and specialists of the International Nickel Company's research and development division ironed out "the bugs" in the mechanism, picking a two percent nickel cast iron as the alloy for both the drive body and the driven body, or outside casing.

Four factors dictated that choice: By using nickel cast iron the friction co-efficient could be maintained. Maintenance of a co-efficient, to within .01%, was basic to the success of the clutch.

Nickel cast iron was easy to machine, homogeneous, simple to cast and free flowing.

Its mechanical properties prevented the possible outer casing burstages that were the one danger point in the clutch.

It was considerably cheaper than competing materials.

Various metals are used for the eight blocks of the driving mechanism, depending on the job. Lead, zinc-alloy and bronze are among those used. Nickel cast iron is specified when excessive slippage is desired because it won't heat-check.

Mr. Wilson makes sure the metallurgical specifications are rigidly adhered to in the foundries that supply his castings. Test bars sent to Inco's laboratories ensure this.

Until recently for outer casings where peripheral speeds in service exceeds 4,000 fpm, nickel cast iron could not be safely used and still maintain safety factor required. In such jobs fabricated mild steel casings have been used. They are difficult to make and very costly.

Now tests have been run using Ductile cast iron in a special service application. The service is an engine drive to a compressor and the clutch is required to transmit 100 hp at 1,500 rpm. The operating rim speed of the clutch is slightly over 7,500 fpm. The clutch "idles" automatically at 500 rpm. The testing unit is so arranged that the compressor unloads every 10 to 12 seconds. This testing unit was kept in constant operation for a period of five weeks, which represents something over three years of exacting field service operation.

At the end of the five week period the clutch was removed for examination and there was no sign of wear in any of the parts of the clutch. The ductile cast iron housing of the clutch was in perfect condition, and no wear had taken place on the friction wall of the driven body nor the block bosses of the drive body.

The clutch was simply replaced in the service again with all of its original parts and underwent a further seven week test.

Test observation of the new cast iron used in the clutches show the following interesting facts:

Standard pattern equipment can be used for its molding in the cast iron foundry.
Its machining characteristics are very much the same as nickel cast iron.

There are fewer rejects of defective castings in the production line.

Friction co-efficient is almost identical with that of the nickel cast iron-a very important factor, as it is possible to use standard rating tables.

It is quite safe to use in clutches operating at 7,500 fpm rim speeds which could never be done with regular cast iron.

Substantial savings are made in material costs for units where fabricated steel was formerly used.

Standard molded castings have more than double the tensile strength of ordinary cast iron and when annealed will meet most exacting requirements for most of the high speed units.

The tests are now planned for clutches made of ductile cast iron to operate at 10,000 fpm.

Like most men with an inventive mind, Mr. Wilson is an individualist. When he first realized the potentialities of his clutch, he decided that he, and he alone, would control its rights and its manufacture. The Automatic Clutch Corp. is N. Bruce Wilson and a handful of enthusiastic young engineers and mechanics, among whom is his son Robert Bruce Wilson. Wilson will not seek outside financing-the company's expansion has come only as he has plowed back the profits. For that reason his manufacturing facilities are not yet under one roof, much of the foundry work being done on contract by other firms. But he foresees the day when all his manufacturing will be consolidated in one plant, when Canadian built BLM automatic clutches will be marketed on a big scale throughout the world.


Careful selection of men appointed to maintenance crews is recommended by the Industrial Accident Prevention Associations with the further recommendation that there should be some direct and continuing effort by plant supervisors to see that maintenance crew-men are carefully instructed and properly supervised on order to prevent accidental injuries.

The memorandum to industry states "A maintenance crew is set up for the specific purpose indicated by its name and the maintenance crew which consists of a certain number of individuals who are likely to be injured is an indication of very bad selection on the part of someone in the organization."

Contact This Company

All Topics