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舊 2004-02-11, 11:36   #1
chao
攀岩癌症患者
 
註冊日期: 2000-07
文章: 619
chao
危險bolt的種類

以下文章及照片出自----http://www.safeclimbing.org/education/dangerbolts.htm

Dangerous Bolts - Bolts to Avoid
by Duane Raleigh

Externally threaded sleeve anchors
You can find externally threaded sleeve anchors in almost any hardware store. These take the same effort to place and cost about as much as the Hilti HSL and Rawl Bolt, but are only about half as strong because their external threads reduce the effective diameter of the bolt where it contacts the hanger, giving it a low bending strength and making it prone to shearing off.

Torque bolts
We didn\'t find any dependable torque bolts, although some climbers use and swear by the USE Diamond Taper Bolt, which can be strong but usually isn\'t. To place a torque bolt you tap the bolt into the hole and then torque it down, spreading an expansion cap at the back of the hole to create a friction hold. Sounds good enough, and USE Diamond touts this anchor as the strongest expansion bolt made, but the problem is these bolts don\'t have any leeway for user error. Torque the bolt too tight and you strip the expansion cap, ruining the placement. Get the bolt too loose and the cap will hold a pullout load about as well as bubble gum on the end of a nail.

We really gave Taper Bolts a chance, setting dozens of them in their optimum substrate, hard rock. We tried to set the bolts by \"feel,\" just as you would when climbing. Half the time we got it right and the 3/8inch Taper Bolts held up to 3000 pounds in a straight pull out. But we blew it with the other half and the bolts slid out of the hole at only 700 pounds. Worse yet, we couldn\'t tell the good placements from the bad until we ripped them all out.

The Wejit Anchor Bolt is another variety of torque bolt, bur fortunately most climbers have more sense than to use it. This anchor has two pushwires running down the shaft that culminate in a pair of tangs that splay out when you crank the bolt down. Tested in shear, the 3/8inch Wejit Anchor Bolt held around 2600 pounds in hard rock but broke or pulled out at an average of 1300 pounds in tensile.

Sleeve-and-nail bolts
The Star Dryvin is the only sleeve-and-nail bolt we found. This anchor, once commonly used in sandstone, utilizes a lead sleeve and a steel nail. You tap the sleeve in the hole, and then hammer the nail in, spreading the sleeve. In the best rock the 3/8inch Dryvin only holds 1400 pounds in shear and less than that in pullout. In sandstone, where Dryvins were thought to be a good alternative for drilled angles these bolts are unbelievably weak-we pulled one out with our fingers.

Rickety and somewhat expensive at $2 each, there\'s no excuse for ever using a Dryvin. If you see a star icon on a nail head that\'s embedded in a sleeve, yank the sucker out and put in a real bolt.

Drop-in bolts
These are the soft lead \"shells\" you see in the anchor department at the hardware. To use these bolts you drill a hole, hammer the shell in, and then screw a machine bolt into the sleeve to expand it. Drop-ins in the 3/8inch and 1/2 inch sizes can be strong, but for the size holes they require (a 3/8inch bolt takes a 1/2inch hole) these anchors are inefficient. Also, drop-in sleeves can crack or strip out when you insert the machine bolt. Save your money for better bolts.

Studs
Stud bolts expand, creating a friction grip, when you hammer them onto an expansion pin set in the back of the hole. We tested Rawl, Star, and Ramset/Red Head stud bolts, although Stud bolt you can find similar bolts from almost any bolt manufacturer.

Stud bolts can be strong in hard rock, but suffer from several maladies that make them unsuited to rock climbing. First, you have to drill the hole to an exact depth to make sure the expansion pin engages the stud. Second, the exposed threads on these bolts makes them subject to work fatigue. Third, you can\'t remove or countersink these anchors without destroying the rock around them. And last, you can\'t buy studs in stainless steel.

Self Drills
The self-drill bolt serves as both a drill and a bolt. Sounds good? It isn\'t.

In medium rock these bolts pull out around 700 pounds. In hard rock the \"bit\" dulls easily and usually two or three are needed to finish the hole. But, in most cases, climbers only drill the bolt half-way before they become frustrated with the system and stop; leaving a hideously weak and botched bolt. Even when placed correctly the strongest self drilled bolt only holds 3000 pounds shear - which is not much considering the amount of effort required to drill the hole and the other


Reprinted from Climbing Magazine.

__________________
----------------------------------------------------------

When I have a little time, I climb;
and if any is left, I eat and sleep.

「攀岩星球」上只住著兩種人,一種是在攀岩的人;
另一種是爬累了正在休息的人。
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