Hello, everyone.

This is Enta.

This is a bit for a down-the-hole hammer.

We have drilled approximately 60 holes using this bit, which has a diameter of about 110 mm, since it was new.

That's how things are right now lol

Here's a side view.

The main unit is already worn out.

Sometimes this happens because of the mountain, and other times it happens because the steel is too soft.

 

You might be thinking, “Is iron really that soft?” but it actually is!

There are several types of hardness tests, but we generally use one called HRC.

Steel Hardness Conversion Table

	Rockwell Hardness (HRC)	Vickers Hardness (HV)	Brinell Hardness (HB)	Shore Hardness (HS)
Soft materials	–	115	110	15
	–	130	125	20
Medium Hardness	–	170	160	25
	–	210	200	30
	22	250	235	35
High Hardness	28	280	270	40
	32	320	300	45
	37	360	340	50
	41	400	380	55
	45	450	430	60
	48	480	450	65
Ultra-High Hardness	52	550	(500)	70
	56	615	–	75
	59	680	–	80
	62	740	–	85
	65	820	–	90

Since I use HRC, I'll proceed with that.

 

Typically, the tips of drill bits are made of tungsten.

This tungsten is second only to diamond in hardness.

So, the hardness of tungsten is around HRC 67 to 80.

 

Please take another look at our Chip. 👆

Only the tungsten is left intact, isn't it?

That means the rock is harder than the bit itself but softer than tungsten.

 

Apparently, the hardness of this unit is HRC 45 or higher, but since it's made in China, I'm a little skeptical lol.

I hear that Japanese-made bits are guaranteed to be around HRC 55, but that means they're expensive, doesn't it...

 

It depends on the condition of the mountain, and bits are consumables.

So, do you go out of your way to find high-quality items? Or do you think that as long as something is usable to some extent, even if it’s cheap, that’s good enough?

It really depends on the person, so I can't say for sure, but I'm going to swap out this bit—this time for an American-made one—and start drilling. lol

 

I don't know how it will turn out, but since the drilling will continue for a while, I'd like to try out a few different things.

 

The hardness of soil is apparently measured on the Mohs scale, with diamond at 15 being the hardest.

If you look at the table below, you'll see that the HRC and New Morse ratings allow you to compare the rock and the bit.

Vickers	Brinell	Rockwell				Shore	Old Morse	New Morse	例
HV	HB	HRA	HRB	HRC	HRD	HS	Reference Values
–	–	–	–	–	–	–	1	1	Talc
–	–	–	–	–	–	–	2	2	Nylon
100	100	–	–	–	–	–	3	3	Polycarbonate
105	105	–	62.3	–	–	–	.	.	.
117	111	–	65.7	–	–	15	.	.	.
122	116	–	67.6	–	–	18	.	.	.
127	121	–	69.8	–	–	19	.	.	.
130	124	–	71.2	–	–	20	.	.	Calcite
132	126	–	72.0	–	–	20	.	.	.
140	133	–	75.0	–	–	21	.	.	.
150	143	–	78.7	–	–	22	.	.	.
160	152	–	81.7	0.0	–	24	4	4	Fluorite
170	162	–	85.0	3.0	–	25	.	.	.
180	171	–	87.1	6.0	–	26	.	.	.
190	181	–	89.5	8.5	–	28	.	.	.
200	190	–	91.5	11.0	–	29	.	.	Cast Iron FC25
210	200	–	93.4	13.4	–	30	.	.	.
220	209	–	95.0	15.7	–	32	.	.	.
230	219	–	96.7	18.0	–	33	.	.	.
240	228	60.7	98.1	20.3	40.3	34	.	.	.
245	233	61.2	–	21.3	41.1	–	.	.	S45C
250	238	61.6	99.5	22.2	41.7	36	.	.	.
255	243	62.0	–	23.1	42.2	–	.	.	.
260	247	62.4	101.0	24.0	43.1	37	.	.	.
265	252	62.7	–	24.8	43.7	–	.	.	.
270	256	63.1	102.0	25.6	44.3	38	.	.	.
275	261	63.5	–	26.4	44.9	–	.	.	S55C
280	265	63.8	103.5	27.0	45.3	40	.	.	.
285	270	64.2	–	27.8	46.0	–	.	.	.
290	275	64.5	104.5	28.5	46.5	41	.	.	.
295	280	64.8	–	29.2	47.1	–	.	.	.
300	284	65.2	105.5	29.8	47.5	42	.	.	.
310	294	65.8	–	31.0	48.4	–	.	.	.
320	303	66.4	107.0	32.2	49.4	45	.	.	SCM440, 445
330	313	67.0	–	33.3	50.2	–	.	.	.
340	322	67.6	108.0	34.4	51.1	47	.	.	.
350	331	68.1	–	35.5	51.9	–	.	.	SUS Beads
360	341	68.7	109.0	36.6	52.8	50	.	.	.
370	350	69.2	–	37.7	53.6	–	.	.	.
380	360	69.8	110.0	38.8	54.4	52	.	.	.
390	369	70.3	–	39.8	55.2	–	.	.	.
400	379	70.8	–	40.8	56.0	55	5	5	Apatite, Spring Steel SUP10
410	388	71.4	–	41.8	56.8	–	.	.	.
420	397	71.8	–	42.7	57.5	57	.	.	.
430	405	72.3	–	43.6	58.2	–	.	.	.
440	415	72.8	–	44.5	58.8	59	.	.	.
450	425	73.3	–	45.3	59.4	–	.	.	.
460	433	73.6	–	46.1	60.1	62	.	.	.
470	442	74.1	–	46.9	60.7	–	.	.	.
480	452	74.5	–	47.7	61.3	64	.	.	.
490	460	74.9	–	48.4	61.6	–	.	.	.
500	471	75.3	–	49.1	62.2	66	.	.	.
510	479	75.7	–	49.8	62.9	–	.	.	.
520	488	76.1	–	50.5	63.5	67	.	.	.
530	497	76.4	–	51.1	63.9	–	.	.	.
540	507	76.7	–	51.7	64.4	69	.	.	.
550	571	77.0	–	52.3	64.8	–	5.5	.	Fuji Glass Beads
560	525	77.4	–	53.0	65.4	71	.	.	.
570	535	77.8	–	53.6	65.8	–	.	.	.
580	545	78.0	–	54.1	66.2	72	.	.	.
590	554	78.4	–	54.7	66.7	–	.	.	.
600	564	78.6	–	55.2	67.0	74	6	6	Feldspar
610	573	78.9	–	55.7	67.5	–	.	.	Zircon
620	582	79.2	–	56.3	67.9	75	.	.	.
630	591	79.5	–	56.8	68.3	–	.	.	.
640	601	79.8	–	57.3	68.7	77	.	.	.
650	611	80.0	–	57.8	69.0	–	.	7	.
660	620	80.3	–	58.3	69.4	79	.	.	Hard Glass Beads
670	630	80.6	–	58.8	69.8	–	.	.	.
680	–	80.8	–	59.2	70.1	80	.	.	.
690	–	81.1	–	59.7	70.5	–	.	.	.
700	–	81.3	–	60.1	70.8	81	.	.	Steel Beads
720	–	81.8	–	61.0	71.5	83	.	.	.
740	–	82.2	–	61.8	72.1	84	.	.	.
760	–	82.6	–	62.5	72.6	86	.	.	.
780	–	83.0	–	63.3	73.3	87	7	8	Quartz, Crystal
800	–	83.4	–	64.0	73.8	88	.	.	SKH High-Speed Tool Steel
820	–	83.8	–	64.7	74.3	90	.	.	.
840	–	84.1	–	65.3	74.8	91	.	.	.
860	–	84.4	–	65.9	75.3	92	.	.	.
880	–	84.7	–	66.4	75.7	93	.	.	.
900	–	85.0	–	67.0	76.1	95	.	.	.
920	–	85.3	–	67.5	76.5	96	.	.	.
940	–	85.6	–	68.0	76.9	97	.	.	.
1000	–	86.2	–	68.9	–	–	.	.	.
1050	–	86.6	–	69.6	–	–	.	.	.
1100	–	87.1	–	70.3	–	–	.	.	.
1150	–	87.5	–	70.9	–	–	.	.	.
1200	–	87.9	–	71.5	–	–	.	.	.
1250	–	88.3	–	72.1	–	–	8	9	.
1300	–	88.7	–	72.7	–	–	8.3	10	.
1350	–	89.1	–	73.4	–	–	.	.	.
1400	–	89.6	–	74.0	–	–	.	.	.
1450	–	90.1	–	74.6	–	–	9	.	.
1500	–	90.5	–	75.3	–	–	.	.	.
1600	–	91.3	–	76.6	–	–	.	.	.
1700	–	91.9	–	77.9	–	–	.	.	.
1800	–	92.6	–	79.2	–	–	.	11	.
1900	–	93.1	–	80.5	–	–	9	12	.
2000	–	–	–	–	–	–	.	.	.
2100	–	–	–	–	–	–	.	.	.
2150	–	–	–	84.0	–	–	.	13	.
2200	–	–	–	–	–	–	.	.	.
2250	–	–	–	85.0	–	–	.	14	.
2500	–	–	–	–	–	–	.	.	.
3000	–	–	–	–	–	–	.	.	.
4000	–	–	–	–	–	–	.	.	.
5000	–	–	–	–	–	–	.	.	.
9000	–	–	–	–	–	–	10	15	Diamond

It's actually pretty interesting if you all take a moment to look into things like the hardness of bits.

Since the bedrock consists of various interlayered strata, it’s hard to generalize, but it is one indicator.

That said, the number of bits you can actually use is limited, and depending on the manufacturer, there are even ones designed for ultra-hard rock, so it’s interesting to ask about the HRC rating, isn’t it?

 

See you later.